View Full Version : Gamma and Zone System

1. What gamma (approximately) corresponds to N, N-1 and N+1 development? How muc h would the gamma change for condensor head versus cold-light head?

2. Is "expose for the shadows and develop for the highlights" still true for mod ern films that have an almost straight curve?

james mickelson

7-Aug-2000, 22:06

#1- who cares? #2- you betcha!

Pete Andrews

8-Aug-2000, 07:28

It's easy enough to work out the gamma, once you've decided what gamma "N" development is for your system, since gamma by definition is logDensity/logExposure.Say it's 0.7 for example. This means that Density increases by 0.7D for every 10 fold increase in exposure. N+1 means that we get that 0.7D increase for a stop less exposure. For only a 5 fold increase. We have to use logs at this point, but those modern thingies with LCDs and numbered buttons should take all the scare out of it. Mine tells me that log 5 = 0.69897. Ah! Call it 0.7, it's only sensitometry after all, nothing serious.So we divide our 0.7D density increase by log 5 (0.7), and (I don't need the electronic thingamajig for this one) the answer's 1. So N+1 development gives us a gamma of 1.Likewise with the N-1 dev. Only this time the exposure needs to increase to 20 times to give us the same density. Log 20 = 1.30103. Divide 0.7 by ~1.3 = 0.53846. And that's our gamma at N-1.Luckily, we don't ever need to calculate those logs again, they're constant for a halving or twofold increase in exposure.

To summarise, whatever the gamma is for N development, it's divded by 0.7 to give the gamma at N+1, and divided by 1.3 for N-1. Now all you've got to do is look up the development times for those gamma values. Ba boom! (All donations gratefully accepted.)

Jeff White

8-Aug-2000, 09:26

1. The average gradients for your question= .54 for N, .46 for N-1 and .67 for N+1. This is figured using the traditional zone placements as outlined in "The Negative". Some people figure using different zones and then these numbers would change. 2. Yes it still holds true. The negative materials have changed but printing paper characteristics are still the same. Sure it is possible to get a grade 00 now but would you really want to print on it?

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